Effect of graphite on the degree of grinding and the structure of α-Fe powder in an ultrasonic mill

Abstract

Methods of Mossbauer spectroscopy, electron microscopy, and optical metallography were used to study the influence of carbon on the degree of grinding of particles of α-Fe powders in an ultrasonic mill in a helium medium. It is shown that the presence of graphite in the process of milling of the iron powder (Fe46C54 at. %) prevents the oxidation of iron particles and contributes to their more significant disintegration in comparison with pure α-Fe. It has been established that the Fe particles with a size of 80–1500 nm are single-crystal and that the structural elements with sizes less than 25 nm correspond to graphite and iron oxides (FeO and Fe3O4). The Mossbauer studies of the powder of pure iron processed by ultrasound showed the presence in the spectrum of components which relate to iron oxides. In the presence of carbon, the processing in an ultrasonic mill for 20 h leads to a line broadening of the spectrum of iron due to the dissolution of carbon, and milling for 50 h led to a wide distribution of the parameters of the hyperfine structure of the spectra, which indicates the formation of a solid solution of carbon in iron and the formation of a carbide phase.